Ultrasound imaging is accomplished by placing an ultrasound transducer on a selected location of a body and projecting ultrasound energy into the body. Acoustic waves reflecting from internal structures in the body are then received by the transducer and are processed to form an image of the internal structures. In a particular ultrasound method, amplitudes of selected harmonics of the returned signal are processed to form the ultrasound image. Briefly and in general terms, harmonic generation by the internal structures in the body is at least partially determined by the properties of the tissue that reflect the ultrasound energy, so that the presence of harmonics in the received echo may be used to generate useful information in the ultrasound image, as discussed in further detail in A. Bouakaz, E. Merks, C. Lancee, N. Bom, “Noninvasive Bladder Volume Measurements Based on Nonlinear Wave Distortions,” Ultrasound in Medicine & Biology, 30:4, pp. 469-476, which publication is incorporated by reference herein.
In selected ultrasound imaging applications, it is often desirable to distinguish between a bodily fluid and an adjacent tissue, or between bodily fluids of different types, such as between blood and various other bodily fluids. For example, when a selected anatomical portion is imaged using B-mode ultrasound imaging, a bodily fluid and certain adjacent soft tissues within the selected portion may be relatively indistinguishable in the resulting image. Moreover, when blood within the selected portion and other bodily fluids are imaged using B-mode ultrasound, images may be generated that similarly fail to properly distinguish the blood from the other bodily fluids.
Accordingly, a new imaging system is needed that permits the diagnostician to easily distinguish or discriminate between different fluid compositions, or between a bodily fluid and tissue. It is further desirable to render more easily detectable in an ultrasound image any boundaries between cavities that contain fluids of different composition, and between a bodily fluid and a bodily tissue.